This application relates to a motor protector circuit for a sealed compressor wherein temperature feedback is provided to the motor protector circuit from the pump unit.
Compressors are utilized in many modern cooling applications. The compressor compresses a refrigerant which is then delivered into a refrigerant cycle for cooling purposes. Compressors are typically mounted in a hermetically sealed housing incorporating an electric motor and a compressor pump unit. The motors are typically provided with a protector circuit which is opened to stop operation of the motor when a particularly high temperature is sensed. In this way, the motor is protected from being operated during unduly high temperature conditions. The presence of an unduly high temperature at the motor is indicative of problems in the system, and thus this provides protection not only to the motor, but also to other areas of the compressor and the refrigeration system.
One known type of protector circuit is used with a motor driven by a single phase power supply. In this type of motor, the windings for the motor stator typically include run and start windings. The two windings are driven by a current, and an electrical phase offset between the two windings causes a rotor associated with a shaft to rotate. This in turn drives the compressor pump unit. The protector circuit associated with this type of motor includes a single common line which passes through a selectively open temperature sensitive switch, and then branches into a line communicating with a start winding heater, which also provides a return for the start windings. The common line also branches into a return for the run windings. When the switch opens, the motor is stopped.
The start winding heater is positioned close to the temperature sensitive switch, such that if the start winding heater increases in temperature, it opens the switch on the run windings.
The above-described protector circuit stops the motor should the run windings experience an unduly high temperature, or should the start windings experience an unduly high temperature or current. Sometimes a small heater is also provided in the run winding branch which provides additional protection in the event of unduly high run winding temperature.
However, there are problems which may exist within the compressor pump unit which are not quickly sensed at the motor. These conditions may allow the motor to operate for an undesirable amount of time until the motor protector circuit acts to shut down the motor. Thus, there is a need for providing fisher sensitivity or feedback to the motor protector circuit.
In a disclosed embodiment of this invention, a system is provided which increases the temperature of the start winding heater when a feedback component elsewhere in the compressor is at an elevated temperature. in this way, the motor protector switch circuit is opened, stopping operation or the motor. In a preferred embodiment of his invention, the feedback component is a switch or positive temperature co-efficient resistor mounted in parallel with the start winding heater. The switch or positive temperature co-efficient resistor is placed in contact with a component in the compressor which is to be sensed.
In one preferred embodiment the feedback component contacts a portion of a scroll compressor. If the portion of the scroll compressor experiences an undesirably high temperature, then the positive temperature co-efficient resistor increases its resistance. Alternatively, the switch is opened if the temperature exceeds a predetermined maximum. Under either condition, the feedback line in parallel with the start winding heater now forces more current through the start winding heater. When the positive temperature co-efficient resistor increases its resistance, more current flows through the start winding heater. If the feedback switch is opened, additional current flows through the start winding heater. In either case, the start winding heater increases its temperature, and causes the main switch on the common line to open.
In alternative embodiments, there may be an auxiliary heater which provides the feedback.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.